Regarding electric double layer capacitors using an electric double layer formed at interface of a polarizable electrode and an electrolyte surface, the demand thereof as memory backup electric power sources has been rapidly growing in recent years. Moreover, attention has been paid to the application thereof to articles for which a large capacity is required, such as power sources for electric vehicles.
An electrode for an electric double layer capacitor has a structure wherein an active material for the electrode, such as activated carbon, is bonded to a current collector with a binder. As the binder for an electric double layer capacitor, there is generally used a fluorocarbon polymer such as polytetrafluoroethylene or polyvinylidene fluoride. If the used amount thereof is small, the binding force to the current collector is insufficient. If the used amount is large, a problem that the internal resistance of the electrode increase is caused. The smoothness of electrodes obtained by use of these polymers is insufficient; therefore, there has been a risk that the electrodes become uneven or the electrodes are short-circuited when capacitors are made therefrom. Against the problems, an attempt is made for supplying an electrode excellent in smoothness and binding force by use of a non-fluorine-contained polymer as a binder. For example, Japanese Patent Application Laid-Open (JP-A)-2002-256129 suggests a binder for an electrode wherein a water-dispersible binder resin and a special thermo-reversible thickener are used.
However, an electrode obtained by applying, to a current collector, the binder for an electrode wherein the special thermo-reversible thickener is used is insufficient in binding force and flexibility but is excellent in smoothness. For this reason, when the electrode is wounded so as to be matched with, for example, the shape of a cylindrical capacitor, its electrode layer is easily cracked or fallen off.